1. Field of the Invention
The present invention relates to a water based pigmented ink for writing, drawing, painting, printing, or marking. The ink is composed of coloring matter, additives, and water as solvent.
2. Description of the Related Art
Inks of this type are known in the art, particularly in the form of water-based marking fluids.
JP 61-268 773, and EP 0 344 379 A2 which is substantially equivalent to JP 61-268 773, describe a water-based, pigmented, luminescent ink, composed of a dyed material which is formed by polymerization of a monomeric emulsion of acrylonitrile, methacrylic acid and styrene. Thus, a polymeric dispersion is obtained with a particle diameter of less than 0.5 .mu.m. This dispersion is dyed with a fluorescent dye. In addition, the ink contains hydrophilic organic solvents, such as ethylene glycol, propylene glycol, glycerin, etc. In the case of this solvent-containing, lightfast ink, which may also be used in micro-encapsulated carbonless copying papers and fax papers, the trace will darken and lose its luminescence after a certain time. This effect happens in some fax papers already within a few minutes. Furthermore, the ink has a relatively short cap-off time of about 45 minutes. Besides, this ink is difficult to wash out of many kinds of fabrics.
European patent application EP 0 374 668 A2 discloses a fluorescent marking fluid which contains at least one coumarinic dye and has an acrylic resin base which is stable at pH 3 to 5.
This fluid does not attack the dyes in other materials, such as, in particular, the triphenylmethane dyes of carbon papers. The lightfastness of these inks is better than in pyronine ink, but still not satisfactory in many cases. Experiments have shown that the trace does not luminesce until after it is dry. The use of organic solvents that have been proposed for the improvement of this ink is to be seen as a further disadvantage.
DE 40 20 900 C1 describes a marking fluid which is based on an aqueous solution of hydroxy-pyrene-trisulfonic acid. Additives used in this writing fluid are saccharose, lactose, maltose as well as their monosaccharides or mixtures of their saccharides. In addition, this writing fluid contains an isothiazolinone derivative as a preservative, a water soluble bonding agent and wetting agents.
A particular disadvantage of this writing fluid is its limited lightfastness, which is common to all pigment-free inks and which, contrary to pigmented inks, is often unsatisfactory.
Further, there are pigmented luminescent inks on the market whose coloring pigments consist of an alkaline dye and of acrylonitrile/butyl acrylate. Additional components in these inks are a preservative, an emulsifier or wetting agent, and water. The disadvantages of this ink are the same as those described above in connection with EP 0 344 379 A2. Here, too, after a certain time there is a darkening and loss of luminescence of the trace on various fax papers, on some papers already after a few minutes. Furthermore, this ink also has a relatively short cap-off time. Likewise, this ink is hard to wash out of many kinds of fabrics.